The invention relates to a compact circuit package mountable to a heat sink in good heat transfer relation.
Compact circuit packages housing power conditioning electronic components must dissipate the heat generated by such components, for example by means of a heat sink. The circuit package typically includes an electrically insulative thermally conductive substrate, circuit means including heat generating components on the top side of the substrate, and an electrically insulating housing covering the substrate and circuitry. The package is mounted to a heat sink such that the heat generated by the circuitry is transferred through the substrate to the heat sink, for example as shown in Kaufman U.S. Pat. No. 4,218,724.
It is desirable to provide for maximum heat transfer from the circuit package to the heat sink. In order to fill the interstices in the substrate and heat sink surfaces, silicon grease has previously been manually applied to these surfaces before mounting to thereby improve heat transfer characteristics. Such grease application was normally done in situ. The circuit package installer dipped his fingers into a container of grease and spread the grease onto the ceramic substrate and the heat sink with his fingers. This was a messy operation, and also required that the installer have a supply of grease readily at hand.
There is a need for a simple, effective technique for providing thermoconductive material at the interface of the heat sink and the circuit package for enhancing heat transfer. One solution is shown in my co-pending Application Ser. No. 06/546,999, filed Oct. 31, 1983.
The present invention provides another solution. In the present invention, the circuit package includes membrane means containing thermoconductive material for rupturing against a heat sink to spread the thermoconductive material along the interface of the circuit package and the heat sink. The membrane means is adhesively stuck to the circuit package and ruptures upon compressive engagement with the heat sink when the circuit package is mounted thereto. The thermoconductive material is automatically applied to the interface of the circuit package and heat sink without manual intervention or a separate step.
In the preferred embodiment, the membrane means comprises a plurality of burstable granules each encapsulating a nodule of thermoconductive material and adhesively stuck to the bottom of the substrate. The granules burst upon pressured engagement with the heat sink to spread the contained thermoconductive material. In an alternate embodiment, a single burstable membrane encapsulates the thermoconductive material and is adhesively stuck to the bottom of the substrate.